Geological, Geomorphological, and Geotechnical Aspects of the Marchand LeveeFailure, Marchand, Louisiana

摘要

This report examines the factors leading to and the mechanisms involved in thelevee failure at Marchand, Louisiana. The report addresses the (a) geology within the pertinent river reach, (b) Holocene chronology of the study area and historic meander of the river, (c) characteristics of the channel geometry in the study reach, and (d) mechanisms of the failure. The failure reach exhibits a clay topstratum about 90 ft in thickness underlain by fine sands. The river incises into the sand to a depth well below the base of the clay topstratum. A three-stage failure mechanism is suggested. The first stage was a retrogressive mechanism in the deep sands which undercut the cohesive overburden. The second stage of failure involved intermittent loss of riverward pieces of the overburden by shear failure, perhaps occurring over considerable time. Following sufficient loss of neutral block shear strength along the critical failure surface, the final failure stage was a massive wedge-type failure along the clay topstratum/sand substratum interface with the levee embankment as part of the active wedge.